This invention relates generally to crop harvesting machinery and has particular reference to devices for separating light admixtures from the cropped material treated by a grain harvesting machine.
Known in the present state of the art cropped material precleaners, comprising a conveying element, sieves and a cleaning fan. The cropped material from under the threshing and separating device is fed onto the conveying element (that is, a grain pan, augers, chain-and-slat conveyer, etc.), which transfers it onto the sieves, wherein stray admixtures (i.e., cavings, chob) are separated from grain.
The above-discussed precleaners are disadvantageous in having comparatively low throughput capacity by the fact that any increase in the rate of feed of the cropped material for such cleaning above the permissible level specified for a given grain harvesting machine causes considerable loss of grain. This prevents the provision of a reliable cleaning unit for high-throughput grain harvesters.
Some prior-art grain harvesters are known to incorporate devices for precleaning the cropped material before its being fed onto the sieves. These precleaning devices are known either in the form of an aspiration duct or as two rubber-clad rolls adapted to throw the cropped material into the air stream. While passing through the above-mentioned precleaning devices the cropped material loses part of the light admixtures, whereby partially cleaned cropped material is fed onto the sieves.
The above-mentioned precleaners are disadvantageous in featuring but low-efficient air-stream separation of the light admixtures from the grain, as the cropped material is separated into fractions only by their aerodynamic properties. As a result, a great deal of grain is carried away along with the light admixtures at higher rates of feed of the cropped material, which likewise impedes the provision of a cleaning unit for high-throughput grain harvesters.